Heat exchanger employing two-stage cross-flow fan



Oct- 25, 1966 N. LAING 3,280,902

HEAT EXCHANGER EMPLOYING TWO-STAGE CROSS-FLOW FAN Filed Aug. 17, 1965 United States Patent L 9 Claims. (Cl. 165122) This invention relates to fans of the cross-flow type. The application is a continuation-in-part of my copending application Serial No. 853,596, filed November 17, 1959, now abandoned.

The invention more particularly concerns fans of the cross-flow type, that is, machines comprising a cylindrical bladed rotor mounted for rotation about its axis in a predetermined direction and defining an interior space, and guide means defining with the rotor an entry region and a discharge region, the guide means and rotor co-operating on rotation of the latter in said predetermined direction to induce a flow of air from the entry region through the path of the rotating blades of the rotor to said interior space and thence again through the path of said rotating blades to the discharge region. More especially but not exclusively, the invention concerns fans of the cross-flow type wherein the guide means and rotor co-operate to set up a vortex of Rankine character having a core region eccentric of the rotor axis and a field region which guides the air so that fiow through the rotor is strongly curved about the vortex core: such fans are sometimes known as tangential fans and the preferred form of fan to be described in detail later is of this type.

The tangential fan is capable of moving large volumes of air, but in its simpler forms does not generate a very high static pressure. This can be a disadvantage in some applications, for example in driving air through a heat exchanger providing substantial resistance to flow.

The main object of this invention is to provide a simple and compact fan of the cross flow type which is capable of generating pressures higher than simple forms of such fans hitherto usually produced.

The invention in one broad aspect thereof, proposes to make use of two cross flow fans in series with a diffusing space in between, so that the total pressure is greater than a single fan of simple design could provide. The rotors of the two fans are of the same length and preferably of equal diameter and are mounted opposite one another for rotation about parallel axes so that flow takes place always in planes perpendicular to the axes. For the sake of compactness it is strongly preferred to have the inlet to the first rotor and the outlet duct from the second facing in the same general direction so that in passing through the fan the air follows a generally U-shaped path. Preferably the guide means for the rotor are formed by portions of two guide walls which with end walls, define the inlet, intermediate space and outlet duct, the whole ducting being readily formed out of sheet metal.

It is a characteristic of the vortex flow above referred to that the major part of the throughput is turned around the vortex core through a substantial angle, normally in excess of 90, in passing through the rotor. This turning of the flow is without the energy losses which would be associated with a similar turn in a duct. In one preferred form of the invention this property is exploited by arranging the rotors to rotate in the same direction and forming the vortex cores adjacent the guide wall on the inside of the U-shaped path. In this way the air can be turned through the U sha'ped path with a minimum of loss of energy.

The rotors can be driven by individual motors, or from "ice one motor through belting or the like. In a further aspect, the invention provides a double A.C. induction motor comprising a single lamination stack, a central winding on the stack, and a pair of armatu-res rotatably mounted at either end of the stator about parallel axes, the stator providing at said ends arms which embrace opposite sides of the armatures. This motor can with advantage be made to drive the two rotors by direct-mounting them on the armature shafts.

Further features, objects and advantages of the invention will become apparent from the following description of two preferred embodiments given by way of example with reference to the accompany-ing diagrammatic drawings, in which:

FIGURE 1 is a transverse sectional view of a two stage fan of the cross flow type;

FIGURE 2 is a schematic end view of the driving motor for the FIGURE 1 fan; and

FIGURE 3 is a transverse sectional view of another two stage fan of cross flow type.

Referring to FIGURES 1 and 2, the fan there shown comprises ducting designated generally 1 comprising first and second guide walls 2, 3 interconnecting plane parallel end walls 4, the ducting co-operating with first and second similar bladed cylindrical rotors 5, 6 mounted opposite one another for rotation about parallel axis and and both extending between the end walls. The ducting 1 defines an inlet 7 for the first rotor 5, an intermediate space 8 between the rotors, and an outlet duct 9 downstream of the sec-0nd rotor 6. The intermediate space 8 has a first portion 10 which diverges in the direction of flow to form a diffuser, leading a second portion 11 forming an entry region for the second rotor 6. At the downstream end of the outlet duct 9, which is also divergent in the direction of flow to form a diffuser, is mounted a heat exchanger shown schematically at 12. A guide vane 13 extends between the end walls 4 in the entry region 11 to help lead air from the diffuser 10 towards the rotor 6.

The rotors 5, 6 each comprise a series of forwardly curved blades 14 supported between end discs 15: the blades extend parallel to the axis and are arranged in a ring thereabout to define an interior space. The directions of rotation of the rotors 5, 6 are opposite and are shown by the arrows 16, 17.

The first guide wall 2 presents to the first rotor 5 a main guide portion 20 subtending a small angle at the rotor axis and defining with the outer envelope of the rotor a gap 21 which in the embodiment shown converges in the direction of rotation. Remote from the rotor 5 the main guide portion 20 merges at a rounded nose 22 with an outlet guide portion 23 of guide wall 2, the portions 20 and 23 defining a substantial angle. Opposite the portions 26, 23 of the guide wall 2, the guide wall 3 provides a portion 24 which diverges steadily from the rotor with increasing radius of curvature. The lines 25, 26 of nearest approach of the wall portions 20, 24 to the rotor 5 define the inlet 7 and are well spaced from the rotor envelope. The wall portion 23 and 24 define the diffuser 10.

On rotation of the rotor 5 in the direction of the arrow 16 the rotor and guide walls 2, 3 combine to set up a vortex having the general characteristics of a Rankine vortex and a core region schematically shown at V which interpenetrates the path of the rotating blades 14 of the rotor nearer to the wall 2 than to the wall 3. The vortex causes a flow of air along paths strongly curved about the vortex core region V, the flow nearer thereto being faster than the flow nearer to the wall 3: faster and slower flow tubes are shown schematically at MF and F.

The second guide wall 3 provides for the second rotor 6 a main guide portion and an outlet portion similar to the wall portions 20, 23 provided by the first guide wall 2 for the first rotor 5 and designated respectively 23'. The second guide wall 3 has a generally U-shaped portion 30 joining the portion 24 thereof co-operating with the first rotor 5 to the main guide portion 20 co-operating with the second rotor 6, the U-shaped wall portion defining the entry region 11 for the second rotor. The first guide wall 2 has a return bend 31 adjacent the second rotor 6 and opposite the U-shaped wall portion 30, where the outlet guide portion 23 merges into a wall portion 24 which diverges steadily from the rotor 6 in the same manner as the wall portion 24 of guide wall 3 diverges from the rotor 5. Wall portion 23 and 24' define the outlet duct 9.

The guide wall portions 20, 23, 24 co-operate with the rotor 6 in the same manner as the wall portions 20, 23, 24 with the rotor 5: vortex core region and flow lines are again shown at V, MP, F.

As will be understood from the foregoing, the inlet 7 and the outlet duct 9 face in the same general direction and thereby the ducting 1 defines a generally U-shaped path for air flowing from the inlet to the outlet duct. Air is deflected from one limb of the U to it bight (i.e. inlet 7 to the space 8) by virtue of the action of the vortex in the first rot-or 5 and (as above mentioned) without substantial energy loss. In passing through the fan the air flow has its static pressure increasedcin both combinations of rotor and diffuser (rotor 5 a fi'd' space 10, and rotor 6 and duct 9) and is thus at a higher pressure than could be obtained in a cross flow fan of simple construction having only one rotor. By virtue of the U- shape of the flow path the arrangement can be very compact.

The preferred form of drivingmotor, of shaded pole A.C. induction type, is shown in FIGURE 2 and comprises a single stator 40 having a stack 41 of strip like laminations carrying a central winding 42. A pair of similar squirrel-cage armatures 43, 44are rotatably mounted one at either end of the stator: the laminations have arms 45, 46 which embrace the armatures.

The rotors, 5, 6 preferably have one end directimounted on the support shaft of each armature 43, 44.

In the second form of two stage fan according to the invention; shown in FIGURE 3, those parts which are similar to parts of the fan just described will be denoted by the same reference numerals and will not need further descriptions. Only the differences between the two fans will be mentioned.

The main difference, so far as the flow pattern is concerned, lies in the fact that in the FIGURE 3 fan the rotors 5, 6 rotate in the same direction and the guide wall portions 20', 23' for the second rotor 6 are provided by the guide wall 2, the portion 24 being provided by the wall 3. This has two main advantages. First, the natural vortex flow in both rotors 5, 6 provides the required turning of the air flow to get it round the U- shaped flow path defined by the ducting. Second, the ducting can be more compact.

A second difference lies in the arrangement in the FIGURE 3 fan of the heat exchanger 12 diagonally across the outlet duct 9, downstream of a short diffusing section 50. This allows the heat exchanger to be spread over a large area compared with the cross section of the duct, and, once again, makes for a compact structure with a minimum of resistance to flow. A grille 51 is provided on the inlet side. The rotors 5, 6 are driven by a belt 52 from a single motor 53.

I claim:

1. A two-stage cross-flow fan comprising first and second cylindrical bladed rotors of equal length mounted for rotation about parallel axes, driving means to rotate the rotors in predetermined directions, and ducting providing end walls generally aligned with the ends of the rotors and guide walls interconnecting the end walls, the ducting defining an inlet for entry of air to the first 4. rotor, an intermediate space between the rotors which diverges towards the second rotor and an outlet duct, the inlet and the outlet duct facing the same general direction so that in passing through the fan the air follows a generally U-shaped path, the guide walls also providing portions co-operating with said rotors on rotation thereof to induce a flow of air from the inlet through the path of the rotating blades 'of the first rotor to the interior thereof and thence again through the path of the rotating blades of the first rotor to the intermediate space, the flow continuing through the path of the rotating blades of the second rotor to the interior thereof and thence again through the rotating blades of the second rotor to the outlet duct.

2. A fan as claimed in claim 1, wherein the outlet duet has at least a portion which is divergent.

3. A fan as claimed in claim 2, wherein downstream of said divergent duct portion is mounted heating means.

4. A fan as claimed in claim 1, wherein said driving means rotates the rotors in opposite directions.

5. A fan as claimed in claim 4, wherein the driving means is an induction motor with a single stator and two armatures.

6. A fan comprising similar first and second bladed cylindrical rotors mounted for rotation about parallel axes; driving means for said rotors comprising an induction motor having a single stator, a central winding thereon, and two armatures one at either end of the stator which in operation rotate in opposite directions, the armatures direct-driving the rotors; ducting providing end walls generally aligned with the ends of the rotors and guide walls interconnecting the end walls, the ducting defining an inlet for entry of air to the first rotor, an intermediate space between the rotors which diverges towards the second rotor and an outlet duct the guide walls also providing portions co-operatingwith said rotors on rotation thereof to induce a flow of air from the inlet through the path of the rotating blades of the first rotor to the interior thereof and thence again through the path of the rotating blades of the first rotor to the intermediate space, the flow continuing through the path of the rotating blades of the second rotor to the interior thereof and thence again through the rotating blades of the second rotor to the outlet duct.

7. A fan comprising first and second cylindrical bladed rotors of equal length mounted for rotation about parallel axes, driving means to rotate the rotors in predetermined directions, and guide means defining an inlet for entry of air to the first rotor, an intermediate space between the rotors and an outlet duct, said space and duct having portions diverging in the directionof flow to form diffusers, and said guide means having portions co-operating with the rotors on rotation thereof to induce a flow of air from the inlet through the path of the rotating blades of the first rotor to the interior thereof and thence again through the path of the rotating blades of the first rotor to the intermediate space, the flow continuing through the path of the rotating blades of the second rotor to the interior thereof and thence again through the rotating blades of the second rotor to the outlet duct.

8. A heat exchanger apparatus comprising end walls, a generally J-shaped outer Wall and a I-shaped inner wall extending between the end walls, said inner and outer walls being spaced to define a duct of rectangular cross sectlon extending between an inlet adjacent the smaller llmb of the J-shaped outer wall and an upwardly directed outlet at the top of the longer limb of the J-shaped outer Wall, a pair of bladed cylindrical rotors mounted within the duct between the end walls for rotation about spaced parallel axes and located between the inlet and outlet, an intermediate space between the rotor, said space diverging in the direction of flow to form a diffuser, drive means to rotate the rotors, the rotors on rotation cooperatng with adjacent surfaces on the inner and outer Walls to induce a flow of air through the inlet, twice through the path of the rotating blades of one rotor, twice through 5 6 the path of the rotating blades of the other rotor and References Cited by the Examiner out of the outlet, a heat exchanger disposed obliquely in UNITED STATES PATENTS the duct and filtering means extending between the end 532,789 1/1895 Ketcher 310-126 X walls and obllquely between the outer wall at the top of 1,482,047 1/1924 Steinbach 310 112 the smaller limb of the J-shaped outer wall and the inner 5 wall at the longer limb of the J-shaped inner wall, the 219-370 filtering means defining with said walls a triangularsection air entry region. FOREIGN PATENTS 9. A heat exchanger according to claim 8, wherein the 559,024 1/1958 g drive means is a single motor driving the rotors by a 10 337,300 5/1959 swltzerland' single belt in the same direction. ANTHONY BARTIS, Primary Examiner. 

1. A TWO-STORAGE CROSS-FLOW FAN COMPRISING FIRST AND SECOND CYLINDRICAL BLADED ROTORS OF EQUAL LENGTH MOUNTED FOR ROTATION ABOUT PARALLEL AXES, DRIVING MEANS TO ROTATE THE ROTORS IN PREDETERMINED DIRECTIONS, AND DUCTING PROVIDING END WALLS GENERALLY ALIGNED WITH THE ENDS OF THE ROTORS AND GUIDE WALLS INTERCONNECTING THE END WALLS, THE DUCTING DEFINING AN INLET FOR ENTRY OF AIR TO THE FIRST ROTOR, AN INTERMEDIATE SPACE BETWEEN THE ROTORS WHICH DIVERGES TOWARDS THE SECOND ROTOR AND AN OUTLET DUCT, THE INLET AND THE OUTLET DUCT FACING THE SAME GENERAL DIRECTION SO THAT IN PASSING THROUGH THE FAN THE AIR FOLLOWS A GENERALLY U-SHAPED PATH, THE GUIDE WALLS ALSO PROVIDING PORTIONS CO-OPERATING WITH SAID ROTORS ON ROTATION THEREOF TO INDUCE A FLOW OF AIR FROM THE INLET THROUGH THE PATH OF THE ROTATING BLADES OF THE FIRST ROTOR TO THE INTERIOR THEREOF AND THENCE AGAIN THROUGH THE PATH OF THE ROTATING BLADES OF THE FIRST ROTOR TO THE INTERMEDIATE SPACE, THE FLOW CON- 